The known BMW Valvetronic valve mechanism, as described for example in EP 1039103, operates in the manner described above and is believed to constitute the closest published prior art to the present invention. In the known mechanism, the intermediate rocker pivots about a point at its upper end which can be moved from side to side by means of a cam. At a point between its two ends, the intermediate rocker carries the cam follower, its lower end being contoured and in contact with the valve actuating rocker.
The valve mechanism described in EP 1039103 suffers from several disadvantages. First, the mechanism requires a special cylinder head that increases the overall height of the engine and can cause packaging problems. Second, the intermediate member is not positively retained in the cylinder head and is merely allowed to free float, being urged against its various contact points (at the cam and at its pivot) by means of a spring. Third, a complex control mechanism is required to enable the valve events of several valves to be controlled at the same time.